Optical communications networks are used to transport large amounts of information attributable to voice, data, and video communications. These communications are in the form of optical signals carried by fiber optic cables.
Optical fiber might be used for long-haul transport between central office hubs of telecommunication providers. The optical fiber infrastructure has begun to encroach on traditional wireline infrastructure as optical fiber is extended closer to customer premises.
For example, fiber has been extended from the central office “to the curb”, i.e., a service node near one or more customer buildings as a result of growing demand for increased bandwidth at a local level. The connection between individual buildings and the service node is completed with traditional wireline medium such as copper wires. An optical network unit (ONU) provided the optical-to-electrical and electrical-to-optical conversion required for interfacing the fiber portion of the network with the copper wire portion. The ONU communicates with an optical line terminal (OLT) at the central office.
Decreasing costs of fiber, increasing demand for bandwidth, and lower infrastructure costs have encouraged extension of the optical fiber all the way to the customer premises. An optical network terminal (ONT) terminates the fiber optic network at or near the customer premises and provides the interface between the optical network and any electrical media.
In order to appropriately direct communications between the appropriate customer premises and the OLT, each ONT may be assigned a unique communication channel. In one approach, the unique channel is realized as a specific timeslot of a time-division-multiplexed (TDM) optical signal. As the demand for greater bandwidth increases, a TDM timeslot becomes inadequate.
One approach for accommodating greater bandwidth is to provide a wavelength division multiplexed (WDM) network where each channel is distinguished by wavelength. The use of the same channel for upstream and downstream communications results in Rayleigh backscattering that impairs bi-directional communications on the same channel.